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how many wires in a box #76491 02/12/01 10:30 AM
Joined: Feb 2001
Posts: 5
pfh73 Offline OP
Junior Member
I am confused on how many wires can go in box. The plastic boxes I have all say for example 8#12 . My question is does this mean maximum 8 12 gage wires including ground or not counting ground wires. I have a 21.0 cu box. Using 12 gage romex. How many con wires can this box accomodate?

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Re: how many wires in a box #76492 02/12/01 10:43 AM
Joined: Feb 2001
Posts: 4
snwire Offline
Junior Member
It is going to depend on wether or not you have a device in it or not. If you have a device you can put 6 #12 and 1 ground(all the grounds count as one) and one device if you do not have a device you can put 8 #12 and one ground

Re: how many wires in a box #76493 02/12/01 07:52 PM
Joined: Oct 2000
Posts: 5,389
sparky Offline
Sometimes the boxes will be marked as the the number of deductions allowed, or in cubic inches, as you have stated.

This is as applied to 370-16
"Number of Conductors in Outlet, Device,and Junction boxes, and Conduit Bodies "

If you can be specific as to your application, we could go there and help you out.
[Linked Image]

Re: how many wires in a box #76494 01/17/02 02:26 AM
How about for metal boxes and BX cable? -Tom-

Re: how many wires in a box #76495 01/17/02 07:03 AM
Joined: Jan 2002
Posts: 1,457
Electricmanscott Offline
It seems like this is always a confusing thing for people but once you get it its actually quite easy to figure out. They seem to have simplified it in the 99 or 96 code to make it a little easier to understand.

Re: how many wires in a box #76496 01/17/02 08:08 AM
Joined: Mar 2001
Posts: 2,056
Redsy Offline
8 #12s would be max. with a blank cover.
You must deduct 2 for the receptacle, 1 for all(not each) of the grounds, and on metal boxes with internal clamps, 1 for all the clamps. This leaves 5, (or 2 cables).
#12 requires 2.25 cu. in. per conductor. If you know the volume, do it that way.

Re: how many wires in a box #76497 01/17/02 10:13 PM
Joined: May 2001
Posts: 129
frodo Offline
the best advice here is to disregard what the box says except for the CUBIC INCH REFERENCE, which MUST be legibily marked. once you know the cubic inch then you can easily look up the amount of volume required for a single conductor type or combined conductor types. and like has been pointed out here dont forget to deduct for devices and a ground...

after you do that a few times you will easily know how to wire any box

hope that helps

planning is the key here

good luck

Re: how many wires in a box #76498 01/17/02 11:28 PM
Joined: Mar 2001
Posts: 2,056
Redsy Offline
sorry, wrong thread.

[This message has been edited by Redsy (edited 01-18-2002).]

Re: how many wires in a box #76499 01/19/02 08:05 PM
Joined: Nov 2001
Posts: 280
motor-T Offline
Just my own personal preference, and it is a little more expensive, but I usually use 4-squares, and if the 2 1/8 isnt enough especially for ceiling boxes I use 4 11/16 it gives you a huge 42 cubic inches and plaster rings for the fixture, as far as I am conccerned the bigger the better.


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